package org.apache.lucene.document;

/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import org.apache.lucene.search.NumericRangeQuery; // for javadocs
import org.apache.lucene.util.NumericUtils; // for javadocs

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;
import java.util.Locale;
import java.util.TimeZone;

/**
 * Provides support for converting dates to strings and vice-versa.
 * The strings are structured so that lexicographic sorting orders 
 * them by date, which makes them suitable for use as field values 
 * and search terms.
 * 
 * <P>This class also helps you to limit the resolution of your dates. Do not
 * save dates with a finer resolution than you really need, as then
 * RangeQuery and PrefixQuery will require more memory and become slower.
 * 
 * <P>Compared to {@link DateField} the strings generated by the methods
 * in this class take slightly more space, unless your selected resolution
 * is set to <code>Resolution.DAY</code> or lower.
 *
 * <P>
 * Another approach is {@link NumericUtils}, which provides
 * a sortable binary representation (prefix encoded) of numeric values, which
 * date/time are.
 * For indexing a {@link Date} or {@link Calendar}, just get the unix timestamp as
 * <code>long</code> using {@link Date#getTime} or {@link Calendar#getTimeInMillis} and
 * index this as a numeric value with {@link NumericField}
 * and use {@link NumericRangeQuery} to query it.
 */
public class DateTools {

    final static TimeZone GMT = TimeZone.getTimeZone("GMT");

    private static final ThreadLocal<Calendar> TL_CAL = new ThreadLocal<Calendar>() {
        @Override
        protected Calendar initialValue() {
            return Calendar.getInstance(GMT, Locale.US);
        }
    };

    //indexed by format length
    private static final ThreadLocal<SimpleDateFormat[]> TL_FORMATS = new ThreadLocal<SimpleDateFormat[]>() {
        @Override
        protected SimpleDateFormat[] initialValue() {
            SimpleDateFormat[] arr = new SimpleDateFormat[Resolution.MILLISECOND.formatLen + 1];
            for (Resolution resolution : Resolution.values()) {
                arr[resolution.formatLen] = (SimpleDateFormat) resolution.format.clone();
            }
            return arr;
        }
    };

    // cannot create, the class has static methods only
    private DateTools() {
    }

    /**
     * Converts a Date to a string suitable for indexing.
     * 
     * @param date the date to be converted
     * @param resolution the desired resolution, see
     *  {@link #round(Date, DateTools.Resolution)}
     * @return a string in format <code>yyyyMMddHHmmssSSS</code> or shorter,
     *  depending on <code>resolution</code>; using GMT as timezone 
     */
    public static String dateToString(Date date, Resolution resolution) {
        return timeToString(date.getTime(), resolution);
    }

    /**
     * Converts a millisecond time to a string suitable for indexing.
     * 
     * @param time the date expressed as milliseconds since January 1, 1970, 00:00:00 GMT
     * @param resolution the desired resolution, see
     *  {@link #round(long, DateTools.Resolution)}
     * @return a string in format <code>yyyyMMddHHmmssSSS</code> or shorter,
     *  depending on <code>resolution</code>; using GMT as timezone
     */
    public static String timeToString(long time, Resolution resolution) {
        final Date date = new Date(round(time, resolution));
        return TL_FORMATS.get()[resolution.formatLen].format(date);
    }

    /**
     * Converts a string produced by <code>timeToString</code> or
     * <code>dateToString</code> back to a time, represented as the
     * number of milliseconds since January 1, 1970, 00:00:00 GMT.
     * 
     * @param dateString the date string to be converted
     * @return the number of milliseconds since January 1, 1970, 00:00:00 GMT
     * @throws ParseException if <code>dateString</code> is not in the 
     *  expected format 
     */
    public static long stringToTime(String dateString) throws ParseException {
        return stringToDate(dateString).getTime();
    }

    /**
     * Converts a string produced by <code>timeToString</code> or
     * <code>dateToString</code> back to a time, represented as a
     * Date object.
     * 
     * @param dateString the date string to be converted
     * @return the parsed time as a Date object 
     * @throws ParseException if <code>dateString</code> is not in the 
     *  expected format 
     */
    public static Date stringToDate(String dateString) throws ParseException {
        try {
            return TL_FORMATS.get()[dateString.length()].parse(dateString);
        } catch (Exception e) {
            throw new ParseException("Input is not a valid date string: " + dateString, 0);
        }
    }

    /**
     * Limit a date's resolution. For example, the date <code>2004-09-21 13:50:11</code>
     * will be changed to <code>2004-09-01 00:00:00</code> when using
     * <code>Resolution.MONTH</code>. 
     * 
     * @param resolution The desired resolution of the date to be returned
     * @return the date with all values more precise than <code>resolution</code>
     *  set to 0 or 1
     */
    public static Date round(Date date, Resolution resolution) {
        return new Date(round(date.getTime(), resolution));
    }

    /**
     * Limit a date's resolution. For example, the date <code>1095767411000</code>
     * (which represents 2004-09-21 13:50:11) will be changed to 
     * <code>1093989600000</code> (2004-09-01 00:00:00) when using
     * <code>Resolution.MONTH</code>.
     * 
     * @param resolution The desired resolution of the date to be returned
     * @return the date with all values more precise than <code>resolution</code>
     *  set to 0 or 1, expressed as milliseconds since January 1, 1970, 00:00:00 GMT
     */
    @SuppressWarnings("fallthrough")
    public static long round(long time, Resolution resolution) {
        final Calendar calInstance = TL_CAL.get();
        calInstance.setTimeInMillis(time);

        switch (resolution) {
            //NOTE: switch statement fall-through is deliberate
            case YEAR:
                calInstance.set(Calendar.MONTH, 0);
            case MONTH:
                calInstance.set(Calendar.DAY_OF_MONTH, 1);
            case DAY:
                calInstance.set(Calendar.HOUR_OF_DAY, 0);
            case HOUR:
                calInstance.set(Calendar.MINUTE, 0);
            case MINUTE:
                calInstance.set(Calendar.SECOND, 0);
            case SECOND:
                calInstance.set(Calendar.MILLISECOND, 0);
            case MILLISECOND:
                // don't cut off anything
                break;
            default:
                throw new IllegalArgumentException("unknown resolution " + resolution);
        }
        return calInstance.getTimeInMillis();
    }

    /** Specifies the time granularity. */
    public static enum Resolution {

        YEAR(4), MONTH(6), DAY(8), HOUR(10), MINUTE(12), SECOND(14), MILLISECOND(17);

        final int formatLen;
        final SimpleDateFormat format;//should be cloned before use, since it's not threadsafe

        Resolution(int formatLen) {
            this.formatLen = formatLen;
            // formatLen 10's place:                     11111111
            // formatLen  1's place:            12345678901234567
            this.format = new SimpleDateFormat("yyyyMMddHHmmssSSS".substring(0, formatLen), Locale.US);
            this.format.setTimeZone(GMT);
        }

        /** this method returns the name of the resolution
         * in lowercase (for backwards compatibility) */
        @Override
        public String toString() {
            return super.toString().toLowerCase(Locale.ENGLISH);
        }

    }

}
